1. Field
This disclosure is directed to novel electrochromic materials and electrochromic devices that use the electrochromic materials. More specifically, the electrochromic materials are viologens into which an imidazole derivative is introduced asymmetrically (hereinafter “benzimidazole-derivatized asymmetric viologens”).
2. Description of the Related Art
Electrochromism is the phenomenon displayed by some materials that reversibly change color when a voltage is applied to them. In other words, an electrochromic material is one that changes color upon applying an electrical field to it. The material undergoes reversible changes in optical properties by an electrochemical redox reaction.
Electrochromic devices that take advantage of the electrochromic phenomenon have various advantages over other materials used in similar applications such as high reflectivity without a need for an external light source, excellent flexibility and portability. Electrochromic materials are also lighter in weight, and are therefore expected to be useful as flat-panel displays (hereinafter “FPDs”). In particular, electrochromic devices are receiving a great deal of attention because they can be used as E-paper, an electronic medium potentially capable of replacing paper.
Examples of the electrochromic materials may include inorganic compounds such as tungsten oxides, molybdenum oxides, and the like, and organic compounds such as pyridine, aminoquinone, azine compounds, and the like. While blue and green electrochromic materials are known (i.e., they are known to exist in the form of nano-electrochromic forms), red electrochromic materials are not yet discovered.
Organic electrochromic materials are disadvantageous when compared with inorganic electrochromic materials in terms of long-term stability, but have advantages in that they can be used in flexible substrates and can also be used to form thin films by wet processing. Based on these advantages, a great deal of research has been conducted on organic electrochromic materials.